Carrier Aggregation (CA) has been specified by the 3rd Generation Partnership Project (3GPP) for Long Term Evolution-Advanced (LTE-A). CA is used to increase the bit rate by allowing multiple carriers to be aggregated and jointly used. Each aggregated carrier is referred to as a component carrier (CC). CA in LTE supports carrier aggregations for both contiguous and non-contiguous CCs.
Several types of CC configurations can be aggregated in CA. FIG. 1 shows first and second CCs 102 and 104 that are intra-band and contiguous with one another. The non-contiguous CCs 106 and 108 of FIG. 1B can also be aggregated. As shown in FIG. 1C, a CC 110 can still be aggregated with CC 112 even though the non-contiguous CCs are in different frequency bands.
In LTE-Advanced, each CC is limited to bandwidths of 1.4, 3, 5, 10, 15 or 20 MHz and a maximum of five component carriers can be aggregated. When using Frequency Division Duplexing (FDD), user equipment (UE) can aggregate different numbers of CCs in the downlink communications from uplink communications. In addition, the carriers that are aggregated can have different bandwidths. However, the number of uplink CCs may not exceed the number of downlink CCs. In addition, for Time Division Duplexing (TDD) in LTE, the number of CCs as well as the bandwidth of each CC is the same for both uplink and downlink.
When CA is configured in LTE-A, each UE is connected to the cellular network through a single Radio Resource Control (RRC) connection. The serving cell that provides this connection is called the Primary Cell (PCell). When CA is active for a UE, any other cells that are used in CA are referred to as Secondary Cells (SCells). SCells are configured for UEs after establishing a connection through the PCell.
The downlink and uplink CCs associated with the PCell are known as the downlink and uplink primary component carriers (PCCs). SCells may be freely added, removed, activated or deactivated, but the PCell can only be changed by a handover procedure. UE connectivity and handover activity is associated with the PCell, and all cell searching in idle or connected mode is performed relative to PCell operating channels.
Certain portions of spectrum are reserved for incumbent users that make limited use of that spectrum. As wireless technologies evolve, the value of radio spectrum increases, and it becomes more economical to share spectrum between users while minimizing interruption to the incumbent users. However, LTE-A does not specify the operation of CA in a spectrum sharing environment.